Extruder



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Reissued Sept. 28, 1954 UNITED STATES PATENT OFFICE EXTRUDER Eugene E.Heston, Akron,

tional Rubber Machinery Company,

Ohio, assigner to Na- Akron,

Ohio, a corporation of Ohio Original No. 2,595,455, dated May 6, 1952,Serial No. 148,235, March 7, 1950. Application for reissue February 8,1954, Serial No. 409,014

Matter enclosed in heavy brackets appears in the original patent butforms no part of this reissue specification; matter printed in italicsindicates the additions made by reissue.

8 Claims.

The present invention, while relating generally as indicated to anextruder, is more particularly concerned with certain improvements in ascrewtype extruder for thermoplastic and like material which render thesame more emcient in operation to produce a superior extruded product,and which in some instances render possible the extrusion of materialswith which difficulty has been heretofore experienced.

Screw-type extruders of the type currently in use are usually providedwith a strainer or breaker plate assembly between the extrusion end ofthe feed screw and the die to hold back unplasticized particles ofmaterial as well as other foreign matter, such \plate also functioningto build up back pressure on the material to promote frictional heating,mixing, and smearing of the material. It has also been proposedheretofore in the extrusion of certain materials such as vinylidenechloride, for example, to omit the strainer plate assembly and in lieuthereof to mount the feed screw for longitudinal ad- Justment in thecylinder and to form the screw with a tapered end portion forcooperation with a conical bore located adjacent to the die orifice andin this way to effect a desired control of the rate of flow of material.As in the other example, there is created an increased back pressure onthe material which surrounds the screw. An extruder of thelast-mentioned type is disclosed in the Allen L. Heston Patent No.2,449,652, dated September 2l, 1948.

One object of this invention is to provide an extruder in which,contrary to the prior extruders aforesaid, the required back pressure onthe material is built up in the early stages of the extruding process toeffect a more eflicient heating, mixing, and smearing of the material.

Another object of this invention is to provide an extruder which hasnovel means therein for effecting de-volatilization of the material andremoval of trapped air bubbles therefrom during the course of the travelof the material through the extruder.

Another object of this invention is to provide an extruder in whichthere is included a narrow annular orifice defined between relativelyrotating parts of the extruder and disposed ahead of the extrusion dieorifice, the material which is forced through such annular orifice beingsub- Jected to a grinding or smearing action to thereby effect a uniformand thorough dispersion or blending of the material.

Another object of this invention is to provide an extruder in which theaforesaid annular 2 orifice is adjustable to enable variation of thegrinding action in accordance with the properties of the material beingextruded.

Another object of this invention is to provide an extruder which hastherein a tempering or low pressure zone through which the devolatilizedmaterial passes prior to extrusion to transform the material to an idealcondition for extrusion and to relieve the pulsation or uneven flow ofthe material as is occasionally encountered in prior art extruderswherein there is choking of the material at the extrusion end and suddenreleasing of the pressure on the material just prior to the point ofextrusion.

Other objects and advantages of the present invention will becomeapparent as the following description proceeds.

To the accomplishment of the foregoing and related ends, said invention,then, comprises the features hereinafter fully described andparticularly pointed out in the claims, the following description andthe annexed drawing setting forth in detail certain illustrativeembodiments of the invention, these being indicative, however,

of but a few of the various ways in which the principle of the inventionmay be employed.

In said annexed drawing:

Fig. l is a cross-section view of one embodiment of this invention;

Fig. 2 is a cross-section view of a modification; and

Fig. 3 is a fragmentary cross-section view of another modification.

Referring now to the drawing and first to the form of the inventionillustrated in Fig. 1, the extruder illustrated therein comprises a baseI adapted to mount a suitable drive motor and speed reduction gearingtherein (not shown). Journalled in said base and extending rearwardlytherebeyond is a drive quill 2 which has a drive gear 3 keyed thereontoadapted to mesh with the motor drive gearing aforesaid.

Coaxial with said quill is a cylinder assembly I comprising for examplea cylinder bushing 5 fixed within said base and which is preferably,though not necessarily, formed with an internally ribbed or threadedbore E, the threads thereof preferably being inclined in the samegeneral direction as the feeding ribs of the feed screw to be describedhereafter. Said cylinder bushing 5 is formed with a lateral feed opening1 adjacent its rear end which communicates with an opening 8 in saidbase, through which openings thermoplastic or like material in pellet,

granular. powder or chip form is adapted to be introduced into saidcylinder bushing.

Secured to said base and extending forwardly therefrom is a cylinderextension 9 coaxial with cylinder bushing 5. Said extension is providedwith a vent III adjacent one end and has secured at the other end asuitable extrusion die I I. Said cylinder extension 9 is preferablyformed with a smooth wall bore I2 therethrough.

Clamped between said cylinder bushing 5 and said cylinder extension 9 isa valve ring Il which is formed with a tapered bore I4V therethroughsmoothly joining the bores B and I2 of said bushing and extension.

Within said cylinder extension 9 and cylinder bushing yIi and extendingthrough said quill I also rearwardly beyond said base I is a feed screwI5. Said feed screw is formed with an extension Il vin cylinderextension D which has a helical feeding rib I1 thereon, said extensionbeing of slight taper as shown so as to be slightly larger at the dieend thereof whereby to define an annular space Il with bore I2 in saidcylinder extension which may for certain materials gradually decrease incross-sectional area in accordance with the reduction in the buik of thematerial as it is advanced through said cylinder extension Iby saidfeeding rib I1.

Adjacent the small end of said extension i8 is a tapered plug valveportion Is disposed within the tapered bore I4 of said valve ring Il andas will hereinafter appear sa-id valve ring Il and tav pered plugportion I9 constitute a valve assembly which upon axial adjustment offeed screw Il provides an adjustable annular orifice Ill to control therate of ilow of material through the apparatus. Said feed screw isfurther provided with a main body portion 2| disposed within cylinderbushing 8, said portion 2| likewise being provided with a helicalfeeding rib I! thereon adapted to advance material forwardly from thelateral feed openin 1 and I toward die I I.

Said feed screw Il is slidably keyed as at Il to said quill l wherebydriving of said quill through gear 3 will effect rotation of said feedscrew.

Longitudinal adjustment of said feed screw IB to vary the size of theannular orifice 20 between the tapered plug 'portion Il and the taperedbore Il in said valve ring II is effected in much the same manner asdisclosed in theaforesaid Allen L. Heston patent, viz. by means of a nut24 which is threaded onto the rear end portion of said quill I and whichbears against the end of said screw through the intermediary of a thrustblock Il fitted into a slot Il in said nut. The rear face of said blockIl bears against the rear wall of the slot Il and the front face ofwhich is shaped to embrace the rear end of said feed screw Il. Extendingthrough an opening 21 in the end of said nut 2l is a conduit Il which isthreaded into said feed screw whereby the latter may be of hollowconstruction and a suitable coolant circulated therethrough to preventexcessive transmission of heat thereto such as would interfere with thefeeding action. The thrust block 2i is provided with a handle 2| bywhich said block may be manipulated during assembly and disassembly ofthe machine. It is to be noted that the thrust of said feed screw Ilduring operation of the machine is transmitted through said block to thequill. said quill being provided with suitable anti-friction thrustbearings (not shown) to withstand such force.

It is to be understood that suitable temperature control zones will beprovided. as for example a cooling zone which herein is shown ascomprising a chamber Il disposed around the feed openings 1 and 8through which s. suitable temperature modifying medium is adapted to becirculated to prevent the material introduced into the cylinder bushingII from becoming "tacky" and sticking to said feed screw and withseparate heating zones provided as by the electric heating units II andI! which during the initial period of operation of the extruder, supplyheat to the plasticized material disposed around said feed screw andwhich during later periods of operation after the apparatus has reachedoperating temperature are shut oil'. In addition to units 3| and 32there may be provided passages Il for circulation of temperaturemodifying medium to dissipate excess frictional heat which is generatedby the working of the material by the screw. Bald cylinder extension 8and die I I may be provided with similar temperature modifying devices.viz. units 32 and passages il.

Having thus described one embodiment of the invention reference will nowbe made to the operation thereof.

Upon rotation of feed screw Il and introduction of material in desiredform through lateral feed openings 1 and l. the action of the feedingrib 22 supplemented by -the action of the ribs l in said cylinderbushing l, if provided. will be to effect compressing of the material toincrease its heat conductivity and to effect frictional heating, mixing,and smearing of the material, the material thus being worked or churnedbeing at the same time advanced toward said cylinder extension l. It hasbeen discovered that for better results the necessary back pressure onthe material should be built up in the very early stages of the process.

In order to obtain such back pressure build-up as well as to secure ascreening or straining action, said feed screw Il is adjustedlongitudinally within cylinder extension a and cylinder bushing I bymeans of nut I4 so as to desirably adjust the annular orifice 2l betweenthe tapered surfaces of the plug portion I 9 and the tapered bore Il.Ihe restriction to free flow provided at this point effects thenecessary build-up of back pressure on the material in the cylinderbushing and because of the relative rotation of said feed screw Il insaid valve ring Il there is effected a screening. homogenizing, and aiinal plasticization of the material by the smearing action of theclosely spaced tapered surfaces.

Thereafter, the material now in a thoroughly plasticized and homogenizedcondition enters cylinder extension I but at a much reduced pressurewhereby the volatile ingredients and trapped air and gas bubbles in thematerial are vented through the vent opening I0 from the very thintubular stream cf material which issues from the aforesaid annularorifice III. Said thin stream of material fills the annular chamber Ilbetween said cylinder extension bore Il and extension IB and saidfeeding rib I1 on said extension advances the material toward die II.Because of the relatively large cross-section of such annular chamber IBand the relatively smaller pitch of the helical rib I1, the material isadvanced rather slowly. As shown, the annular body of material thusadvanced slowly and at desired pressure becomes slightly thinner towarddie II in order to compensate for the reduction in the bulk thereof andthus maintains a uniform rate of flow. The plasticized material afterflowing through this so-cailed "tempering" zone finally enters and nilsthe chamber adjacent die Il and then is extruded at a uniform pressurethrough said die.

In the form of the invention illustrated in Fig. 2, the cylinderassembly 34 is of integral form. and the tapered bore 35 between thetemperaturecontrol zone 36 and tempering zone 31 cooperates with thetapered portion 38 of feed screw 39 to control the rate of flo-w ofmaterial therethrough and thus to control the :back pressure build-up inthe zone 35 and along the main portion 40 of said feed screw. A furtherdifference in the Fig. 2 construction is that the die 4| and said feedscrew 39 are provided with tapered bore and tapered extension portions42 and 43 respectively which are spaced further apart than the taperedportions 35 and 38 which constitute the flow control valve so that thepressure buildup is in the zone 36 where desired rather than in thetempering zone 31 between the vent 44 and die 4I.

With respect to the helical ribs 6 in the cylinder bushing which aspreviously indicated may be included or not, as described, arepreferably inclined in the same general direction as the feeding rib 22of feed screw I5 whereby to induce a counterflow of the material whichcreates turbulence and thus facilitates more thorough blending o-rmixing and working of the material. Such counterilow, as indicated,improves the mixing and blending characteristics of the extruder so thatthe material as it emerges from the flow control valve orifice 20 is ina thoroughly plasticized and worked condition ready for tempering andelimination of bubbles :by passage at low pressure through the cylinderextension 9. The modification illustrated in Fig. 2 may also be formedwith an internally threaded or ribbed bore 45 to cooperate with the feedscrew as Just indicated.

As a further feature of this invention the tapered plug valve portion I9in Fig. 1 or the corresponding portion 39 in Fig. 2 may, if desired, beprovided with a helical rib 46 of opposite inclination to the feedingrib 22 on screw I5 (or the rib on screw 39 in Fig. 2). Such rib 46creates additional mixing action at the control valve due to grinding orsmearing action and counterilow action t-hereat to supplement orsupplant similar action along the preceding portion of the screw.

In Fig. 3 is shown a modification in which the cylinder bushing 41 isformed with a smooth bore 48 therethrough as distinguished from thebushing 5 in Fig. 1 which has a threaded bore 6 therethrough. In suchmodification, that is the Fig. 3 modification, the counterflo-w actionof the material may be entirely dispensed with when extruding certainmaterials or it may be found that by providing the ribs 46 on the valveportion sufficient counterflow action is obtained so as not to requirethe threaded or ribbed bore 6. In any event, it is within thecontemplation of this invention to only provide feeding ribs on the feedscrew without the counterflow action afforded by ribs 6 or 4E.

Other modes of applying the principle of the invention may be employed,change being made as regards the details described, providing thefeatures stated in any of the following claims, or the equivalent ofsuch, be employed.

I therefore particularly point out and distinctly claim as my invention:

1. An extruder comprising a cylinder having a feed opening at one endfor the introduction of Cil material to be extruded from the other endthereof, a feed screw rotatable in said cylinder and adapted whenrotated to advance and to condition the material for extrusion, and flowcontrol means between the ends of said screw impeding free flow ofmaterial along said cylinder and screw and thereby building up a backpressure on the material in advance of said flow control means, saidflow control means comprising opposed tapered surfaces on said screw andin said cylinder, said cylinder and said screw, in advance of said flowcontrol means, being of smaller diameter than beyond said flow contro-lmeans and such tapered surfaces joining the large and small diameterportions of said cylinder and screw respectively.

2. An extruder comprising a cylinder having a feed opening at one endfor the introduction of material to be extruded from the other endthereof, a feed screw rotatable in said cylinder and adapted whenrotated to advance and to condition the material for extrusion, and flowcontrol means between the ends of said sere-w impeding free flow ofmaterial along said cylinder and screw and thereby building up a backpressure on the material in advance of said flow control means, saidflow control means comprising opposed surfaces on said screw and in saidcylinder which are movable toward and away from each other to vary thesize of the passageway therebetween upon relative axial adjustment ofsaid cylinder and screw, and means for adjusting said cylinder and screwaxially with respect to each other.

3. An extruder comprising a cylinder which includes a feed opening atone end for the introduction of material to be extruded from the otherend and successive zones along which the material is adapted to beadvanced from such feed opening for plasticizing and working while underpressure in one zone and for conditioning for extrusion while under asubstantially reduced pressure in the other zone, a feed screw extendingthrough such successive zones and provided with a feeding rib forcontinuously advancing the material through such zones upon rotation ofsaid screw, and a flow control means between such zones operative tomaintain a backpressure on the material in such one zone and to pass thematerial at a lower pressure to such other zone, said iiow control meanscomprising axially spaced .and opposed surfaces on said feed screw andin said cylinder respectively, defining a passageway therebetween forflow of material from one zone to the other zone, said screw beingmounted for axial adjustment in said cylinder whereby to vary thespacing between such opposed surfaces and thus to vary the size of thepassageway, and means for locking said screw in desired axially adjustedposition in said cylinder.

[4. An extruder comprising a cylinder having a feed opening at one endfor the introduction of material to be extruded from the other endthereof, a feed screw rotatable in said cylinder and adapted whenrotated to advance and to condition the material for extrusion, and flowcontrol means between the ends of said screw impeding free flow ofmaterial along said cylinder and screw and thereby building up a backpressure on the material in advance of said flow control means. said owcontrol means comprising opposed surfaces on said screw and in saidcylinder defining a passageway therebetween of cross-sectional area lessthan that between adjacent portions of said screw and cylinder, saidfeed screw being formed with a rib along its passageway defining surfaceinducing counterflow of material for intimate mixing and blending of thematerial prior toand during now through said ilow control means] 5. Anextruder comprising a cylinder having a feed opening at one end for theintroduction oi material to be extruded from the other end thereof, afeed screw rotatable in said cylinder and adapted when rotated toadvance and to condition the material for extrusion, and ilow controlmeans between the ends of said screw impeding free flow of materialalong said cylinder and screw and thereby building up a back pressure onthe material in advance of said now control means. said now controlmeans comprising opposed tapered surfaces on said screw and in saidcylinder.

[6. An extruder comprising a cylinder having a feed opening at one endfor the introduction of material to be extruded from the other endthereof, a feed screw rotatable in said cylinder and adapted whenrotated to advance and to condition the material for extrusion, ilowcontrol means in the intermediate portion of said extruder providing apassageway which impedes free ilow of material and thereby builds up aback pressure on the material in advance of said now control means, andmeans for varying the flow area of such passageway includingpassageway-defining surfaces relatively movable closer to and furtherfrom each other whereby the ilow area of such passageway may be variedto predeterminedly impede free ilow oi material therethrough inaccordance with the characteristics of the material being extruded] [7.An extruder according to claim 8 characterized further in that ventmeans are provided in the intermediate portion o! said -extrudertoilowing said flow control means for discharge o1 volatile ingredientsand trapped gas bubbles in the material prior to extrusion of thematerial from the other end of said cylinder.]

8. An extruder according to claim 2 characterized further in that saidcylinder in advance of said flow control means is formed with internalhelical ribs inclined in a direction. to induce counterlow of materialin said cylinder and thereby to eiect intimate blending o! the materialprior to advance thereof through said now control means.

9. An extruder according to claim 2 character- 8 ized further in that arib is formed on at least one oi said opposed surfaces disposed toinduce counteriiow of material for intimate mixing and blending of thematerial prior to and during now through said ilow control means.

10. An extruder comprising a cylinder, a feed screw rotatable in saidcylinder, and now control means in an intermediate portion of saidextruder efectiva to impede free flow of the material being extrudedalong said cylinder and screw and thereby to build up a back pressure onthe material in advance of said flow control means, said flow controlmeans comprising axially spaced and relatively axially movable surfaceson said screw and in said cylinder defining a completely annularpassageway of cross-sectional area less than that between adjacentportions of said screw and cylinder, said feed screw being formed with arib along its annular passageway defining surface egective to inducecounterfiow a! the material ,for intimate blending and mixing thereofprior to and during ,flow through said flow control means.

11. An extruder comprising a cylinder, a feed screw rotatable in saidcylinder, flow control means in an intermediate portion of said extrudereective to impede free flow of the material being extruded along saidcylinder and screw and thereby to build up a back pressure on thematerial in advance o! said flow control means, said flow control meanscomprising complementary axially spaced annular portions on said screwand in said cylinder respectively defining a flow control passagewaytherebetween, and means for adiustably varying the axial spacing betweensaid annular portions to thereby vary the flow area of such passagewayso as to predeterminedly impede free )low of material in accordance withthe characteristics thereof.

References Cited in the file of this patent or the-original patentUNITED STATES PATENTS Number Name Date 1,283,947 Steinle Nov. 5, 19181.936.050 Gordon Nov. 14, 1933 2.200.997 Royle May 14, 1940 2,449,652Heston Sept. 2l. 1948 2,496,825 Henning Feb. 7, 1950 2,519,014 BankeyAug. 15, i950 2,015,199 Fuller Oct. 2B. 1952

